damnnnn, i cant believe an arowana cant survive at least a few hours without a filter, and since its 2 feet long, that must've took lots of time and work to make an arowana grow to that size, this kinda tells me that ur gravel/ornaments, etc have not too much nitryfying bacteria, because in my tanks if my filters stop working, my fishes can survive days without it, they may get sick, especially my ghost knife fish and my needlefish, but really that was one weird way to die, couldn't u just change like 10% of the water every 90 minutes or so?